Merge branch 'build_cmake' of https://github.com/TcT2k/wxWidgets

Add CMake-based build system.

Merge the original branch without any changes except for resolving the
conflict due to moving the contents of .travis.yml to a separate file by
propagating the changes done in this file since then to the new script
and rerunning ./build/update-setup-h and ./build/cmake/update_files.py
to update the file lists changed in the meanwhile.

Closes https://github.com/wxWidgets/wxWidgets/pull/330

build/cmake/README.md

@@ -0,0 +1,85 @@
+This directory contains [CMake][1] files needed to build
+native build files for wxWidgets.
+
+For building wxWidgets or using wxWidgets in your CMake project please see
+the [CMake overview](../../docs/doxygen/overviews/cmake.md) in the wxWidgets
+documentation.
+
+CMake files organization
+========================
+All CMake files are located in $(wx)/build/cmake additionally there is a
+_CMakeLists.txt_ in the root directory.
+
+Files
+-----
+* $(wx)/CMakeLists.txt
+    * This should only contain commands and definitions which need to be
+      contained in the top level and includes _main.cmake_
+* config.cmake
+    * Generates config files used to find wxWidgets by other build systems
+    * Creates wx-config
+* files.cmake
+    * List of source files generated by _update_files.py_ from _$(wx)/build/files_
+    * This file should **never** be edited manually
+* functions.cmake
+    * contains various wxWidgets specific functions and macros used throughout
+      the CMake files
+    * Every function should contain a short description of it's parameters as
+      a comment before the function/macro
+* install.cmake
+    * Handles defintions for the ´install` and `uninstall` target
+* init.cmake
+    * Intializes various variables used during the build process and for
+      generation of setup.h and configuration files
+* main.cmake
+    * Includes all other cmake files
+* options.cmake
+    * All user selectable build options should be defined in this file via
+      calls to `wx_option()`
+* policies.cmake
+    * [CMake policies][2] for wxWidgets should be defined in this file
+* setup.cmake
+    * Handles all tests required to create the _setup.h_ header based
+      platform and user settings
+* setup.h.in
+    * Template for _setup.h_ updated automatically by _$(wx)/build/update-setup-h_
+* source_groups.cmake
+    * Define source groups used in supported IDEs
+* toolkit.cmake
+    * Define toolkit specific options and detection to this file
+* uninstall.cmake.in
+    * Used by _install.cmake_ when creating the `uninstall` target
+* update_files.py
+    * Creates _files.cmake_ from _$(wx)/build/files_
+
+Sub directories
+---------------
+Each sub directory contains a _CMakeLists.txt_ and might contain various other
+_.cmake_ files.
+
+* demos
+    * Defines build targets for demos via `wx_add_demo()`
+* lib
+    * Defines build targets for all libraries and bundle third party libraries
+    * Each library is contained in a seperate directory and uses
+      `wx_add_library()` to define the library target
+    * Bundled third party library without upstream CMake support are defined in
+      a _.cmake_ file using `wx_add_builtin_library()` to define static library
+      targets
+* modules
+    * Includes CMake modules used to find third party packages via [find_package()][3]
+    * Includes the [cotire module][4] used to for precompiled header generation
+* samples
+    * Defines build targets for all samples via `wx_add_sample()`
+    * Defintions for trivial samples are included in _CMakeLists.txt_ more
+      complex samples might have a seperate .cmake file
+* tests
+    * Defines build targets for all tests
+* utils
+    * Defines build targets for all utilities
+
+
+[1]: https://cmake.org
+[2]: https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html
+[3]: https://cmake.org/cmake/help/latest/command/find_package.html
+[4]: https://github.com/sakra/cotire/